Fibroblast growth factor 4 (FGF4) is a member of the fibroblast growth factor (FGF) family that possess broad mitogenic and cell survival activities and play key roles in growth and survival of stem cells during embryogenesis, tissue regeneration, and carcinogenesis. FGF4 was identified by its strong oncogenic transforming activity and is a potent angiogenic factor, expressed in several highly vascularized tumors and also in adult mouse testis, intestine, and brain. Studies on the mouse homolog suggests a function in bone morphogenesis and limb development through the sonic hedgehog (SHH) signaling pathway. Furthermore, FGF4 regulates neural progenitor cell proliferation and neuronal differentiation. Recent studies show a growth-promoting role for FGF4 in human embryonic stem cells and a putative feedback inhibition mechanism by a novel FGF4 splice isoform that may serve to promote differentiation at a later stages of development.